Frequency converters using a transmission line impedance transformer



March 21, 1967 R. w. ANDERSON 3,310,747

FREQUENCY CONVERTERS USING A TRANSMISSION LINE IMPEDANCE TRANSFORMER Filed April 12. 1965 f 2000 me f =18OO mc Pk; 23 r- INPUT H 1&1] L. l L

f 200 me I LOCAL o OSCILLATOR OUTPUT INVENTOR RICHARD W. ANDERSON FREQUENCY CONVERTERS USING A TRANSMIS- SION LINE IMPEDANCE TRANSFORMER Richard W. Anderson, Los Altos, Ca]if., assignor to Hewlett-Packard Company, Palo Alto, Calif., a corporation of California Filed Apr. 12, 1963, Ser. No. 272,671 4 Claims. (Cl. 325-445) This invention relates to apparatus for mixing selected frequencies to obtain an intermediate frequency with negligible loss of signal power.

The principal object of the present invention is to provide apparatus for selecting and mixing applied signals with a minimum of signal power loss.

It is another object of the present invention to improved signal filtering and mixing apparatus.

In accordance with the illustrated embodiment of the present invention a pair of cavities are connected to reoeive an applied signal and a local signal and are adapted to resonate at frequencies which are separated by a desired output frequency. The cavities are coupled together using a cable having a length which is a selected multiple of half wavelengths of the applied signal. The ends of the cable form coupling loops within the cavities. One end of the cable passes through the cavity connected to receive the applied signal and connects to a mixing element. Thus the signal coupled to the cable from one cavity and the signal from the other cavity are combined provide in a mixing element to form the desired output fre-' quency.

Referring to the drawing, there is shown a local oscil lator 9 coupled into cavity 11 by a harmonic generator 13 and a coupling loop 15. Applied signal appearing at input 17 is coupled into cavity 19 by coupling loop 21. The cavities are connected together by a cable 23, one end of which forms a shorted coupling loop 25 within cavity 11. The other end of cable 23 passes through the cavity 19, forms a coupling loop 27 therein and connects to mixing element 29. The local oscillator 9 and harmonic generator 13 produce a signal frequency'which resonates in cavity 11. A portion of this signal is picked up by coupling loop 25 and is applied directly to the mixing element 29 by the cable 23. To this signal there is applied the resonant frequency of the signal within cavity 19. Mixing element 29 combines these signal frequencies and produces an output signal as a selected modulation product of the two signals. The length of the cable 23 is selected to be substantially equal to a number of half wavelengths of the signal frequency of r the resonant cavity 19. Thus, for the values indicated, the length of line 23 may be chosen as ten half wavelengths of the signal of cavity 19. This length of line is thus one half wavelength at the frequency of the output signal. Since the cable is shorted at one end by coupling loop 25, the signal in cavity 19 also sees a shorted cable a number of half lengths away from this shorted end. Thus substantially none of the signal power United States Patent 3,310,747 Patented Mar. 21, 1967 ICC The signal coupled from cavity 11 and applied to the mixer element 29 through cable 23 appears with suflicient signal level to properly bias the diode 31 within the mixer element for high sensitivity detection. Applied signals appearing in cavity 19 at low power levels are adequate to produce the desired output signal once the diode is from the applied signal of 17 is coupled from cavity 19 a first cavity resonator connected to the input for receiving an input signal and a second cavity resonator connected to receive the signal from said source;

the first and second cavities having resonant frequencies which are separated by a selected frequency value;

a signal mixer element;

an electric wave transmission line having one end dis posed in signal coupling relationship to the second cavity resonator and having a portion thereof disposed within said first cavity resonator in signal coupling relationship therewith with another end connected to said signal mixer element;

said transmission line having a length between the first and second cavity resonators which transforms the impedance presented by said second cavity resonator to signal on said transmission line having a fre quency equal to the resonant frequency of said first cavity substantially to a short at the location of said portion of the transmission line which is coupled to said first cavity; and

means connected to said signal mixer element for producing an output signal 'of said selected frequency value.

2. Signalling apparatus comprising:

an input and a source of signal;

a first cavity connected to said input and a second cavity connected to said source, said cavities being adapted to resonate at frequencies which are separated by a selected frequency value;

an electric wave transmission line connecting said cavities;

one end of said transmission line being disposed within the second cavity and forming a shorted coupling loop therein;

a mixer element, a portion of said transmission line being disposed within the first cavity to form a coupling loop therein with the end of said transmission line connected to said mixer element;

the length of said transmission line between cavities being substantially equal to a selected multiple of one half wavelength of signal in said transmission line having said selected frequency value; and

means connected to said mixer element for producing an output signal of said selected frequency value.

3. Signalling apparatus as in claim 2 wherein one of 3 4 the first and second cavities resonates at .a frequency for tially to a short circuit at the location along the which said transmission line between cavities is an integer transmission line disposed Within the first ymultlp of P Wavelengths'. References Cited by the Examiner 4. Signalling apparatus as in clalm 3 wherein. the length of said transmission line between cavities is 5 UNITED STATES PATENTS altered from substantially ten half Wavelengths at the 2,616,037 10/ 1952 Wheeler et al 325-445 resonant frequency of said first cavity to transform the impedance presented by said second cavity at the KATHLEEN CLAFFY Pr'mary Exammer' frequency of resonance of the first cavity substan- R. S. BELL, Assistant Examiner. 

1. SIGNALLING APPARATUS COMPRISING: AN INPUT AND A SOURCE OF SIGNAL; A FIRST CAVITY RESONATOR CONNECTED TO THE INPUT FOR RECEIVING AN INPUT SIGNAL AND A SECOND CAVITY RESONATOR CONNECTED TO RECEIVE THE SIGNAL FROM SAID SOURCE; THE FIRST AND SECOND CAVITIES HAVING RESONANT FREQUENCIES WHICH ARE SEPARATED BY A SELECTED FREQUENCY VALUE; A SIGNAL MIXER ELEMENT; AN ELECTRIC WAVE TRANSMISSION LINE HAVING ONE END DISPOSED IN SIGNAL COUPLING RELATIONSHIP TO THE SECOND CAVITY RESONATOR AND HAVING A PORTION THEREOF DISPOSED WITHIN SAID FIRST CAVITY RESONATOR IN SIGNAL COUPLING RELATIONSHIP THEREWITH WITH ANOTHER END CONNECTED TO SAID SIGNAL MIXER ELEMENT; SAID TRANSMISSION LINE HAVING A LENGTH BETWEEN THE FIRST AND SECOND CAVITY RESONATORS WHICH TRANSFORMS THE IMPEDANCE PRESENTED BY SAID SECOND CAVITY RESONATOR TO SIGNAL ON SAID TRANSMISSION LINE HAVING A FREQUENCY EQUAL TO THE RESONANT FREQUENCY OF SAID FIRST CAVITY SUBSTANTIALLY TO A SHORT AT THE LOCATION OF SAID PORTION OF THE TRANSMISSION LINE WHICH IS COUPLED TO SAID FIRST CAVITY; AND MEANS CONNECTED TO SAID SIGNAL MIXER ELEMENT FOR PRODUCING AN OUTPUT SIGNAL OF SAID SELECTED FREQUENCY VALUE. 